Automatic trunking system.



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' AUTOMATIC TRUNKING SYSTEM.

APPLICATION ULEB MAR. 17. 1918.

Fatented Oct. 13

A. E. KEITH.

AUTOMATIC TRUNKING SYSTEM.

APPLICATION PILBD MAR.17, 1918.

1,1 1 3,354. Patend 001.13, 1914 za ,1; "l GRA/5x5.

nNrfrED sTATEs PATENT OFIC.

LEXANDER E. KEITH, OF HINSIALE. ILLINQIS, ASSIGI-OB. TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLIT'JOIS, A CORPORATION OF'ILLINOIS.

AUTOMATIC TRUNKING SYSTEM.

specification of Letters Patent.

Application fiie' Marca x7, 1918. serial No. 754,803.

To all 'w/iom 'it may contra-'1112:'

Be it known that I, ALnafAxm-:a E. lKl-:x'ri-i, a citizen of the United States of America, and resident of 'l'linsdale, in the county of Dupage and State of illinois= have inx'ented certain new and usefu Improveinents in Automatic Trunking Systems, of which the following is a specification.

My invention relates to automatic telephone systems in gainer-'al` and more particu' larly to: a provision in such systems for giving dillierent classes 'of service to different lines which are served by the. same unit of appai'fatus at the central ollice, such as .a line switchboard.

This difference in the ('.liaraeter of service 'furnished to subscril ers has heretofore. been accomplished by havingr single. line service, two party line service or four party lin service. lt often happens. however, that there. may be in a certain district a small number of Subscribers desiring these three kinds of service, and itmay be. desirable to install a small subexchange for this distri'ct. If there are only a small number of subscribers who desire party line, service. or service the eilnivalent in ellieiency to such party line service. it ivo' 'd be souuwhat expensive to install regnlar party line `selec'tivc. sigualin;r apparatns in this subexchange. ln order to give these various classes of service. -under these conditions.l l haveV devisei'l an art-angeinent in which each snbscriber connected to the snl'excha'nge. bas an individual line` and the. distinction between the various classes of service ar-ises in connection with the number of trunh linesl extending' out of this snbexebanle which are. accessible to a particular siibscriber`s line. un;in 'r that there are ten trunk lines` extendiug from this sul.'e.\'.'hau;'e to the. central ollice` the Snbscriliers` who pay for .single line. service ill be fiven access' to an v one of the. ten trnnk lines: those snbscribers who nierelv desire the e|uivalent of two party service will be. ;given access' to a lesser number ol' tlie.-'e. outgoing trunlis. say live: while those who nierely wish the eiuivalent of 'four party line service. will -l'e given access lo a still leszer number of these outgohr;r trunks. say four.

ln this application l have,illustrated my inrention in connection with what. is known as a line'switch s \"lemr-that a system in which each subscriber-z line ir; provided with a switch which automatically' selects an idle trunk extending to a first selector. "l`he line switches employedare vdivided into groups` each group ,being Controlled. b'v i master switch for controlling the operation of the line iswitchesof its group. Where a plurality of these groups of line snnches have access to the same group of trunls, as in my present invention, it becomes necessz'iry to provide 'special means .for proriding 'uardwing'` potentials over the trnnk lines in order to prevent oneswitch from niakin;r connection with a trunk line' with which a second switch has already made connection. i

These. and other objects of-m invention will be more readily understood bv reference to the aceompanj'ing drawings, injwhicl Figures 1, 2 and 3 taken together rep`e-: sent a calling suhseriberis station ;A connected' with a called subscribeifis station'. Figt l is a liagrammatical sltetch showing the, lrnnkinfz arrangenicnt of a system enrbodf lingz the principles of my im'entioii.l

',l`he snbscriberis ap'paratus and the ceniral otliee switches shown herein are of the types well known in 'the prier art. The general `[n'inciples of oi'ieralion of the snbsei'iber's app-zralus i.' disclosed in United States lietlers i'atent to l'l. l). Fali-s No. 866,639, issiaed Heplember QL '1907. 'l'lie general prini'iples of operation of the lini` and master srfitehes are (lis-closed in the lll'rs'r'rlr /zlcf/l'r'rir'n. ol' January 2G, 1905i. and the Sei lecler and connector switcbes are of the general tvpes disclosed iu l7nited States Letters l'atem Nos. 815.512! and fils'hl'l'i. respeclively. granted March lI-l7` lSlO. to Keith7 l'lrickson and l'riek::on.

V'l`'l1e subsi-riliers sations and represenled herein comprise the folln'nfing`r parts: the reeeiver '3, lransmiiter 3. switch book 4. impuls'e wheel impulse. springsI andtl'i; ;frcimd post S. ringer 9. condeuser 10; rel 12156 'spriugs ll. I:) and 13 and a dial (net shown):

on a dial shafl ll. to which latter therefis conductors 24 and '25. The line switch for the called subscriberls station A' is represented at C' (Fig. 3) and is identical with the switches C, D and E. In F ig. 1 there are shown three line switches C, D and E belonging to three different groups, which groups are' provided with master switches F, G and H, respectively.` The master switch that eontrols the line switches C' is not shown in the accompanying drawings, but is .of the same type as the switches F, G and H.

The selectors S and T are of the well- 'known type and consist generally of the line relays 33 and 34, Vertical magnets 35, rotary mfagnets 36 and the back-release relays 39. They are Aalso provided with the side switch wipers 40, 41, 42 and 43. The connector switch U (Fig. 3) is of the general form well known in the prior art and comprises the usual line relays 26 and 27, Vertical and rotary magnets 28 and 29, release magnet 30,

'trunks, and another to just four.

private magnet 31 and the ringer relay 32.

In a system of the general character described herein the lines and their individual switches have heretofore been divided into groups of one hundred each and all have access to the full complement of trunks leading out of such groups. By my present invention, however, the service of certain of the lines is soinewhat restricted, a certain percentage of -the subscribers hein' given greater trunking facilities than ot ers, as will be hereinafter pointed out.

Fig.l 4 represents a plurality of groups of line switches, one group having access to the full complement of trunlr lines leading thercfrom, another to five of those same These three groups of switches may be mounted upon a single frame or Keith unit if (lesired. For the sake of convenience we will say that the group of line switches to which the switch C (l'ig. l) belongs has access vto the trnnks I to R, inclusive, and the group of line switrhes to which the switch l) belong-1 has access to the trnnks N to R. inclnsire. and the group to which the line switch l helongs has access to the trunks (l to li. inclnsii'e. 'It is thus seen that the group of :-,\\.'ii:h(-,s to which the switch helongs has access to live trunk lines that are individual io said switches, and to one lrunk which in turn is accessihle to onc other group of line switchcs, namely, the l`) group and also to the reinaining trnnks ()----ll, whirh are :icc'\ssihle to the groups of switche, to \\'hi'.h the sWitChcS C, I) Mid i'l belong. llnch of the line switches shown is providwl willi the nsual hridge-zgnt-olf rclay .^'0 v trip niagnet 51 and release magnet 'l'hc hride-cnt-oll" relay controls the springs .325, 54. und 5:3, while the trip inagnct 5 .'31 controls the bank Springs 5G to G23, inclusive. through the medium. of the plnngcr. As clcarly descrihcd in the article in the Western E lectric'ian above referred to, these line switches, upon being released, are not immediately picked up by the master switch, but their plunger stands in front of the trunk with which they were last in connection until the master switch in its operation again picks up this line switch. Heretofore a guarding potential was provided to pre-- vent two line switches from making connection with'the .same trunk. In the prese'nt instance, however, it is necessary to provide still additional means, namely, to prevent a line switch in a group controlled by a second master switch from making connection with a trunk before which a line switch of another group is standing. Without such provision it will beseen that one line switch might make connection with a trunk, and then ifthev subscriber fwhose line switch was standing in front of the same trunk made a call, both'subscribers would come in on the same trunk. In order to prevent this I allot to each of the common trunk lines N-R a trunk relay G4 (Fig. 1) for each group of line switches that has access to said common trunk. In Fig. 1 there is shown the trunlc line O, which is common to three groups of lineswitches. Therefcre three such relays G4, 71 and 72 are shown. The trunk line N (Fig. 4) is common to two groups and so would have two such trunk relays -allotted to it. The trunlr lines I--M being accessible only to one groupfof line switches, it is not necessary to provide such a relay for these trnnks. The function of the relay 64 is to niaintain a guarding potential on the master switch bank contacts'of the trunk all the time a plnnger is released from`said trnnk but not yet 'picked np hy the plunger guide shaft, and so climinating .the possihiliy of any other suhso'riber occupying the Sanu: trnnk opposite which the said plunger is onl 1 partially rcslorrd to its normal position. Duringr the time the line switch is artnally ronum'tcd with ,the trunk, the (fuai'ding potential for the trnnk is extended from the hntlcry ll over the conductor 100, release mngnct of 'the line switch (J (which is of low resistance), springs (30 and (11. 'onlnf|`,.:r GG lo the contact T5 05 the lnasl'cr switch l", and also 'from the condnctor (o through the u'inding ('17 of the trlmh' rolny (il (which also has :L low resistance) to the condnctor (38, and through the windings (f) and T0 ot the trunk relays 'il andji'i lo the lnnslcr .switch bank conlaets T21 nnd 7-l of the inuslcr switchrs (l and ll. A fler the line switch is released and before its plnngi'r is pirhcd np l the phmger shal't. the (nzu'ding potential is nlaintaincd on the nxnstcr swilrh hank contact in lhe l'o'lloving nninin'r: When [hc `line switch is released, us will appear lnlcr` the lrnnk rolny become-s enrrgized and .forms :i lockin'g circuit for itself in order that it may remain energized after the Springs 60 and 61 have been separated. This circuit extends from ground Gr*5 through the resistance 'coil 78, Springs 79, 81 and 80, through the winding 82 of the relay 64: to the battery lead 100. In its energized position the relay 64 maintains a guarding potential on the master switch contacts 75, 73 and 74 over the following paths: The guarding po-- 73 and 74. w If a switch belonging to one of the groups to which the switchcs C or D belong has obtained connection with the trunk line and has been released therefrom, the corresponding relay 71 or 72 operates in the same manner as explained for the vrelay 64 to maintain'the guarding potential on the master switch banks until the plunger of the released line switch has been picked up by its guide shaft. In `general whenever any line switch is released from 'one of the trunks which is common to a plurality' of groups of line switches, the relav which' operates to maintain the 'guarding `potential on the master switch ,bank contacts is the particular one of the relays allotted to said trunk which is associated with the master switch of the group to which the line switch which has been released belongs.

The operation of this type of system is well known and fully described in the patents and publication referred to, and it is accordingly not thought necessary to give a detailed description of the 'sa-me, except in so far as relates to the operation of the line and master switches, which operation has hecn slightly changed to provide for-the additional guarding potentials hereinabove refcrred to. The first step which the calling subseriber takes is to remove his reccirer from the switch hook, which separate thespring 19 from the projcction 90 of saidv switch hook, thus breaking the ringer circuit, and by the same operation the springs 20 and 21. make. contact, thereby closing the primary eircuit through the transmitter 3, and the springs 18 and 17 make contact to close the talking Circuit. The subscriber now opcratcs his dial in the usual manner to operate the central ollice switches for the first digit. Ii``his operation removes the lockingI cam 1,:(3 and allows the ground spring -S'l to ,come into contact withthc ground post 8 and sends a preliminary impulse oier the rotary side of the line. by means of the spring 7 being pressed against the ground post 8 by the impu'lse tooth 91, whereupon the trip magnet 51 becomes energized to release the plunger into its bank terminals, pressing together the Springs G0 and (31, G2 and 68, 58 and 59 and and 57. The circuit extends rom the ground post 8 to the spring 7, conductor 24, Springs 53, 51- and 55, magnet 51 and Springs 92 and 93 to the battery lead 100. Upon the Springs 62 and G3 and 56 and 57 making contact, the subscribefls line is extended to the first selector. By the engagerient of the Springs 58 and 59 a guarding potential is placed on the private normal 93, which tcrmin'ates in the private banks of the connector switch through which the calling subscriber is reached. T his potential furthermore causes the bridge cut-off relay 50 to be enirgized, thereby removing the short circuit from across the calling line by opening the springs 53, and lVhcn the Springs 60 and 61 make contact, guarding potentials are also established at the master switch bank contacts 75, 73 and 74, which are tov prevent the trunk Q from being cngaged while busy. vWhen the call is made it will bc assumed that the wiper 95 is resting on and making electrical connection between the common sefrment 00 and the contact 75,'thus establishing a circuit through the lower winding of the relay 1052. lVhen this relay energizes the circ'uit which is the means for supplying battery current to the group of line iswitches represented by the switch C is opened, and the circuit of the motor magnet 105 is closed, whereupon said magnct energizes and operates its armature to rotate the ratchet wheel 108, which operates the plunger guide shaft in the well known manner and moi'es all idle plungers onto a. nonbusy trunk, when the oil-cuits of the motor magnets are broken and the plungers come to rest. It will be seen that in Fig. 4 there are live bank terminals in one group, to which tern'iinals there are no trunk lines connected, and in another group there are six like terminals, The plungers to which these terminals belong are kept 'from coming to rest oppositc these so-called empty trunks by the coi'rrsponding contacts in the master switch bank being provided with a permar'ient guarding potential by either connerting' same to positive or to neatire battery, as the relay 102 and those corresponding to it are so wound that they will respond to either. So it is seen that 'it would he impossible for the plungers to stop opposite these tcrminals. Upon the Springs 50 and ST, (32 and (33 being pressed together, the line coudiuztors 2+. and 25 of the substation A are extended to the first sclcctor S, which is in a position to receive the impulses l'or the lirst digit, when the dial has been pullcd around as far as the finger stop will permit. l'Vhen the dial is released the im-. pulses are then sent over the line to operate the first selector in a manner well understood, and the subsequent Operations of the calling dial operate the second selectors and eonnectors, all in the manner Well understood, to establish connection between the calling and called subscribers, lines. lWhen the sebserihcrs replace their receivers upon the hooltsthe connector switch U and selector switehes T and S are released in the usual manner. When the release magnet ;ii of the. selector S energizes, a circuit is closed through ground G1, Springs 148, trunk-release eonductor 185, relay 146, contact springs l-l), conductor 68, winding 67V of the relay of, springs G1 and and the release magnet 52 of the line switch C to the battery' lead 100. The release magnet 52, upon encrgizing, rcleases the line switch in the usual manner. The relay HG, u'pon energizing, places grounddirect upon the condnctor US a-nd suhstitutes the resistance 175 for the winding U7 of the relay and the release magnet l`his action of the relay LLU insures a good release of the line switch C.

It willlie scen that the winding 67 of the relay (14 is included in the circuit through the releaso'magnet 52 of the line switch (J. This relay is conscquently energized upon the closure of this Circuit when the switch C is released and operates to maintain a guarding potential upon the master switch (-.ontacts of the trunk from which the line `switch C was just released, until the plungcr of .said'switch is picked up l v the pluuger guide shaft. already' liccn stated, this is to prevent the pluugers` engaging with a trunk line that has a plunger .standingr opposite said trunl; in an off-normal condition.

ln order to remove the guarding potential when the line su'itch is again piched up l v the master switch l. providtl an auxilialjv private bank reprcscntcd by the comm.n scgnufnt -l;`() and the wiper lol. This is accomplishcd by the auxiliary private \viper 1531 oscillatiug back onto the contact u'hich corresponds to the trunk terminal omnis-ile, which there. is standing a plunger not. yet. picked up by the. pluuger guide shal'l. Thisl complctesa/rircuit from battery l by u'ay of the, common segment lot), u'iper 151, contact I) and resistance coil 78 to ground G5, thus short-circuiting the coil H'J of the relay (34, which relay thercby de-.

eucre'izes and removes the alove-mentioned t'uardiu;r potential from the contact c, thereliy allou'iug idle plnng'crs to come to rest o; positc said trunks.

lt will t-hns le scen that l have provided a very useful and ellicient trunliujr scheme vrlu'rchy various ('lasses of Service can lie' given to a number of .suhscribers without As has necessitating the employment of selective signaling apparatus used in connection with party line service.

While I have illustrated my invention in connection with one particular type of telephone system, it is, of course, understood that my invention is of broader scope and that I do not wish to lim myself to the particular type of switches vinployed, or to the particular Character of the system.

lVhat I claim as my invention is:-

1. In a telephone system, a plurality of groups of suhscribers' lines, a single group of trunk lines, means whereby certain of said subscribers lines can `connect with any .one of said trunk lines, and means whereby certain other of said subscribers7 lines can connect with a lesser number of said trunk lines.

2. In a telephone system, a plurality of groups of subscribers lines, a group of trunk lines, means Whereby certain. of said'subscribers can select the first idle trunk line out of all of said group of trunk lines, and means whereby certain other of said subscribers have access to a part onlyl of said trunk lines and are provided with means for selecting an idle one of said trunk lines.

3. In a telephone system, a plurality of groups of subscribers lines, a group of trunk lines, a .switching mechanism for each subscriberls line for automatically selecting idle trunks, means wherebycertain of said` switching mcchanisms have access to all of said trunks, and lmeans ivhereby certain other of said switehing mechanisms have access` to hut part ofsaid trunks.

lu a telephone, system, a plurality of groups of subscrihe'rs lines, a group of trunk lines, a line switch for each of said suhscribers7 lines, a master switch controlling a group of said line switches, whereby said line. switches are adapted to connect with an idle trunk, and. means whereby certain of said line switches have access to all of said trunk lines, while other of said line switches have access to but part of said trunk lines.

In a telephone system, a plurality of groups of z-:ahscribers lines, a group of truuk lines, means whereby the subscribers of one of .said groups can connect with any of .said trunk lines, means wherclrv the subsrri'hers iu another of said groups can connect only with a les-:er number of said trunk lines.| means whereby the. suliscrihers of a third group can connect only with a still lesser nun'iber of said trunk lines. and 'means for preventing suhscribers of different groups from couneetiug with the same trunk line.

(i. ln a telephone system, a plurality of groups of suhserihers, lines, a group of truul: lines, individual switchingz mechani-m by which said'subscrilxers can connect with idle trunks, means whereby the switching mechanisms of the subscribers, in one group have access to all of said trunk lines, means whereby the switching mechanisms of the subscribers in a second group have access to but part of said trunk lines, and means for preventing the subscribers of one group from making connection with a trifnk line with which a subscriber of the second group is connected.

7. In a telephone system, a plurality of roups of subscribers lines, a grou of trunk ine's, a line switch for each of sai Subscribers' lines, a master switch in each of said groups for controlling the line switches, said line switches comprising a contact arm adapted to make connection with certain trunk lines, said arms being controlled by said master switch to enable them to automatically connect with an idle one of said trunk lines, means whereby the subscribers of one of said groups have access to all of said trunk lines, means whereby the subscribers of another of said groups have access to but part of said trunk lines, and means for preventing the subscriber's of one group from making connection with a line with which the subscriber of another group is connected.

8. In a telephone system, a plurality of groups of trunk lines, a plurality of groups of line switches, one of saidgroups of line switches having access to all of said trunk lines and another grou having access to but one group of trunk lines, a master switch for controlling each group of line switches, means for controlling said master switches to move said line switches opposite idle trunk lines, and means for then Operating a line switch to connect with a selected trunk.

9. In a telephone system, a plurality of groups of trunk lines, a plurality of groups of line switches, one of said groups of line switches having access to all of said trunk lines and another group having'hccess to but one group of trunk lines, a master switch for controlling each group of said line switches, means for controlling said master switches to move said line switches ,opposite idle trunk lines, means for then operatiiig a line switch to connect with a selected trunk, and means for placing a guarding potential on said trunk While in use.

10. In a telephone system, a plurality of groups of trunk lines, a plurality of groups of line switches, one of said groups of line switches having access to all of said trunk lines and another group having access to but one group of trunk lines, a master switch for controlling each group of said line switches, means for controlling said master switches to move said line switches opposite idle trunk lines, means for then Operating a line switch to connect with a selected trunk, means for disconnecting a line switch from said master switches when it is operated, and means for placing a guarding potential on said trunk while said line switch is co'nnected with the same.

11. In a telephone system, a plurality of groups of trunk lines, a plurality of groups of line switches, one of said groups of line switches havingaccess to all of said trunk lines and another group having access to but one group of trunk lines, a master switch for controlling each group of said line switches, means for controlling said master switches to move said line switches opposite idle trunk lines, means for then operating a line switch to connect with a selected trunk, means for disconnecting said line switch from said master switches when said line `switch is operated to connect with a trunk, means for releasing said line switch from said trunk, means for thereafter again connecting said line switch with said master switches, and means for placin a guarding potential on said trunk until said line switch as again been connected with said master switches.

Signed by me at Chicago, Cook county, Illinois, this 5 day of Marcli 1913.

ALEXANDER E. KEITH.

Witnesses:

ARTHUR J. RAY, EDWARD D. FALEs. 

